Combined tension and screw-down control for strip mills



G. E. STOLTZ Nov. 3, 1942.

COMBINED TENSION AND SCREW-DOWN CONTROL FOR STRIP MILLS Filed Aug. 17,v 195e Patented Noir. 3, 1942 COMBINED TENSION AND SCREW-DOVVN CONTROL FOR STRIP lMlLLS v Glenn E. AStoltz, Edgewood, Pa., assigner to West- I inghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsyl- .vania Application August 17, 1938, `Serial No. 225,353

3 Claims.

My invention relates, generally, to control sys- Y tems for rolling mills, and, more particularly; to

a system of coordinated control for both the screw-down setting of the rolls of a strip rolling mill and the tension on the strip as it passes through such a mill.

It is common practice, in the productio-n of steel strip, to reduce the strip by passing it through `reducing roll stands, and applying tension to the strip as it passes through the roll stand. This method reduces the number of rolling passes in a single stand mill and the number of roll stands in a'tandemmill necessary to produce a given reduction in the strip. The method also imparts desirable characteristics to the finished strip not. otherwise obtainable.

It has also been proposed to control the amount of reduction of the strip by varying the tension on the strip in response to a thickness measuring device, thus maintaining a uniform strip thickness. Such a system is disclosed in the application oi G. P. Lessmann,` Serial No. 151,483, led July l, 1937, r-z'w Patent No. 2,268,217, issued December 30, 1941. However,

' the tension which is applied to a strip must have an upper limit since there is danger of breaking the strip or causing .'nec king or reduction in i the Widthof the strip if the strip tension is too great.4 On the other hand, if the strip tension is too small the desired strip characteristics proof strip be produced while maintaining the strip tension .within predetermined limits.

An object of myinvention, therefore, is to provlde a control 'system for a striprolling mill which shall function to produce av strip of a predetermined lthickness while maintaining strip.

tensions withinpredetermined limits. p l

Another object of the invention is to provide a control system for a strip rolling mill which shall function to so control the screw-down setting of v the reducing rolls and the tension on the-strip as to produce a strip of a predetermined uniform thickness. l

A further object oi the invention ist@ provide a controlsystem for a strip rolling mill which shall function to control the amount o'f tension on the strip in response to the thickness of the strip within predetermined limits of tension and to control the screw-down setting of the reducing rolls. in response to variations of the strip tension beyond the predetermined limits.

-justable lpressure regulating valve I2.

shall function to control both the tension on the strip and the screw-down setting of the reducingrolls, which shall be simple and eilicient in.

operation and inexpensive to manufacture, in-

stall and maintain. i v

These and other objects and advantages of my invention will be apparent from the following detailed description taken in connection with the accompanying' drawing in which:

Figure 1 is a diagrammatic illustration of a control system for a strip rolling mill embodying the principal features of my invention, and

Fig. 2 is a diagrammatic illustration of a fluid pressure operated control device which may be employed in the control system of Fig. 1. f

Referring to Fig. 1 of thedrawing. a tension ing device 4 is provided for applying tension to the strip 6 as it passes in the direction indicated by the arrow between the reducing roll stands 8 v and Ill.l IThe tensioning device 4 is pneumatically operated and the tension applied to the strip by the tensioning device is governed by the ad- The'adjustment of the valve I2 to apply the proper pressure to the tensioning device 4 is regulated in accordance with the thickness of the strip by means of a thickness gauge I4 which actuates a regulator I6 connected to control the adjustduced by-tensioning'the strip will notbeobtained. It is desirable that a uniform thickness Another object of the invention is to fprovide y I a control system for a strip Vrolling mill which ment'of the regulating valve I2. The deflection of the strip 6 by the tensioning device 4 is kept within predetermined limits by controlling the speed of the driving motor 20 of the roll stand I0 by means of as'regulating device I8 which may function to control the field excitation of the driving motor 2 0 toincrease or decrease the 4speed of motor 20 as'may be required. The operation of the tensioning device 4 under control of the adjustable regulating valve I2 in response to variations in thickness of the strip as measured by the thickness measuring device I4 and the action of regulator I6 to control the adjustment ofthe regulating valve- I2 .and the regulator I8 to control the Speed ofthe roll stand motor 20, are fully set'forth in the abovereferred to Lessmann patent, to which reference' is made for complete explanation of the operatio-n of the separate-elements of these devices.

In order that-'too great a tension or t'oo small a tension may not be applied to the strip 6 by the tensioning device 4,`a screw-down device 22 `is provided. This screw-down device is operable to vary thes'p'acing of the rolls of the roll stand B-.in accordance with predetermined variations of the thickness of the str ip 6 and is controlled by the thickness-measuring device I4 through a limit switch 24 and reversing switch 26.

The tension device 4 may comprise a roller 28 supported on one end of a bell crank 36 to bear against the strip 6 deflecting the strip 6 with a transverse force, and thus tensioning the strip. The bell crank 3l) may be operated by a piston 32 which, in turn, operates -under iiuid pressure,

'such for example, as air pressure in the cylinder 34, the tension applied to the strip dependf ing upon the pressure of the air in the cylinder prises generally two rotary contact members 38 which bear against the strip and which are connected in series Acircuit relationwith one leg of a Wheatstone bridge 40, so that the variations in the thickness of the strip will vary the resistance of this leg of the Wheatstone bridge and thus vary the constant flow in the coil of a solenoid 42 connectedacross the bridge. The armature of the solenoid 42 actuates an arm 44 which carries control contacts for the regulator I6 which, in turn, function to govern the current flow in the coil of solenoid 36.

It isto be understood that the thickness responsive device I4 herein shown and described is merely included by way of illustration of an operative device to perform the function of measuring the strip thickness, and that the invention is not limitedto ythis particular thickness responsive device. Any suitable thickness responsive device which will perform the desired function may be used in the combination. Such a` thickness responsive device as that shown in the patent-to Winne 1,969,536, issued August '1, 1934, may be used in place of the device described herein.

The defiection of the .bell crank 30 by the tensioning device 4 controls the regulator I8 to vary the current iiow in the field winding 46 of the motor 2li so that the speed of roll stand I0 may be increased when the deflection of the strip 6 becomes too great and decreased when the de ection of the strip becomes too small.

In order that the tension applied to the' strip by the tensioning device 4 may not be too great and thus cause breakage or necking of the strip,

or too small and thus cause ineicient rolling due to insufiicient tension, or fail to provide the desired characteristics of the strip which are produced by the tensioning, the s crew-down device 22 is varied in accordance with predetermined ,variations in thickness of the strip 6 to keep the `tensionI within predetermined limits.

The screw-down device 22 comprises a motor 43 which are connected in circuit with the wind` ings or relays 50 and 52, respectively.

In order that the screw-down motor 48. may

be lnched or provided with predetermined limited periods of energization, a'time delay relay 60 is connected in circuit with the operating relays of the reversing switch 26. The time delay relay '6U comprises an operating coil and a movable contact element 'I8 anda dash pot 18, the dash pot 'I8 providing time delay in opening and time delay in closing of the relay. The circuit for the coil of the relay 50 extends from one side oi the source of energy indicated by the plus and minus signs through the conductors 62 and 64, the winding of relay 59, conductor 66, contact elements 56 and 54, conductor 68, contact element 'Ill of relay 59, the winding on relay 6D and conductors 'I2 and i4 to the other side of the source of energy. The circuit for the relay 52 of the reversing switch 26 extends from one side of the source of energy through the conductor 62, the winding of relay 52, conductor 76, contact elements 53 and 54, the conductor 66, contact elements "III, the coil of relay 66 and conductors 'I2 ,and 'I4 to the other side of the source of energy.

In the operation of. this control system for the screw-down of roll stand 8, when the thickness measuring device I4 moves the arm 44 in response to increase in thickness of the strip 6 until the movable Contact element 54 engages the iixed contact element 58, a circuit will be completed through the coil of relay 52 causing the energization of the armature of the motor 48 through the reversing switch 26 to reduce the spacing between the reducing rolls of the roll stand 8. At the time that the contact elements 54 and 58 engaged they also completed a circuit through the coil of time delay relay (illA and after a predetermined time determined by the setting of the time delay device 18, the contact element 'I0 will move to open-circuit position to deenergize the relay 52 of the reversing switch 26 and thus deenergize the armature of the motor 48 and stop the screw-down operation. The movement of the contact elements 'I0 to the open circuit position will also deenergize the coil of' the time delay relay 60 and after a predetermined time, depending upon the setting of the time delay device 18, the contact element 'I0 will again move to closed circuit position.

If, at this time the reduction f the strip has not decreased sufliciently to cause the thickness measuring device I4 to move the contact element 54 out of engagement with the Contact element 58, the armature of the motor 48 will again be energized and the relay 60 will again be energized as above described. Thus, the motor 48 will receive periods of energization limited by the time delay relay 60 until the proper spacing of the reducing rolls of the roll stand B has been secured and the thickness measuring device I4 has moved its arm 44, so that the contact element 54 will no longer engage the contact element 58.

In a like manner the thickness gauge I4 will respond to predetermined decreases in the thickness ofthe strip 6 and actuate the armature of the motor 48 through the reversing switch 25 to increase the spacing of the reducing rolls of the roll stand 8. v

Thus the tensioning device 4 will maintain a tension upon the strip 6 proportional to the thickness of the strip, under control of the thickness measuring gauge I4, but when this thickness increases above a predetermined amount or decreases 'below a predetermined amount, thel thickness measuringV device I4 through limit switch 24 will adjust the reducing` roll spacing of the roll stand 8 through the screwdown device 22, so'that the thickness of the strip may be increased or decreased in the reducing rolls to again allow the proper range of tension to be applied to the strip E under the control of the thickness measuring device I4.

It will be seen that the thickness of the strip controls the pressure in the operating cylinder 34 of the tensioning device 4, and thus controls thc tension on the strip E. It will thus be seen that the screw-down may be controlled in accordance with the pressure in the cylinder 34, since this is a Vfunction of the tension on the strip 6.

,In Fig. 2 I have shown a control system for the reversing switch 26 which comprises a Bourdon tube 80 connected in a suitable manner to the conduit between the regulating valve I2 and the cylinder 34 and actuating a movable contact element 54'. Fixed contact elements. 56' and 58 are situated in the path of movement of contact element 54 so that the contact elements 54' and 58' will engage when the air pressure in the cylinder 34 exceeds a predetermined amount and the contact elements 54' and 5B will engage when the air pressure in the cylinder 34 becomes less than a predetermined amount. Suitable adjusting means are provided for the contact elements E' and 58 in orderto provide any desired range y of movement of the contact element 54".

The movable contact element 54' is mounted on a pivoted arm 55 which is connected to be actuated by the Bourdon tube 80 against the bias of a spring member 51. In order to provide 'a reasonable deflection of the movable contact element 54' at the low pressure ranges and lowv tension ranges, a solenoid 59 is provided. The solenoid 59 has its winding connected to a suitable source of energy through a rheostat 6I which may be actuated toprovide the desired energization of the solenoid. 'I'he core of the /solenoid .'59 is connected to the arm 55 so that the pull of the solenoid opposes the bias of the spring 51. Thus the solenoid may be made to assist the Bourdon tube any desired amount in actuating the movable contact element 54', so that the same rangeA of movement of the contact element 54' maybe provided at 10W pressures as at high pressures by merely adjusting the rheo- -stat 6I.

Control circuits 6E', 68 and` 'I6' connected to the contact-elements 565, 54 and 58', respectively, correspond to the corresponding control circuits 66, 18 and 68 of Fig. 1, and the device functions ing rolls in response to variations in the strip tension beyond the predetermined limits, whichshall be simple and efllcient in operation, and inexpensive to manufacture, install and maintain.

lmeans for applying tension to a strip of material `as it passes through the mill, said tensioning means comprising a pressure uid operated means and means whereby variation of the. uid pressure will vary the tension on the'strip. means for varying the fluid pressure in accordance with variations of the thickness of the strip, means for varying the spacing of the reducing rolls of the mill, and means for operating said spacing varying means in accordance with predetermined variations of the fluid pressure, said means for operating said spacing varying means comprising a fluid pressure responsive'device acting against a normal bias, and means for adjusting the degree of said bias to provide a substantially constant range of movement of said uid pressure responsive device regardless of the range of fluid pressures applied to said fluid pressure responsive device.

2. In a control system for a strip rolling mill, pressure fluid operated means bearing on the strip with a transverse force to subject the strip to a tension proportional to the fluid pressure acting on the pressure fluid operated means as the strip passes between adjacent work devices of the mill, regulator means for maintaining a substantially constant uid pressure acting on to control the reversing switch 26 in the manner the pressure fluid operated means, strip thickness responsive means for varying the regulator setting to thereby vary the strip tension in response to variations of strip thickness, and means responsive to predetermined variations of strip thickness for varying the-screw-down setting of the mill. y a

- 3. In a control system for a strip rolling mill, pressure fluid operated means bearing on the strip with a transverse force to subject the 'strip to a tension proportional to the fluid pressure acting on the pressure uid operated means as the strip passes between adjacent work devices of the mill,

. means responsive to the strip thickness for varying the fluid pressure acting on the pressure fluid operated device to thereby vary the strip tension, in accordance with variations of strip thickness,

and means responsive to predetermined variationsin the fluid pressureactlng on the. pressure fluid operated means for varying the spacing of".

the reducing rolls of the mill.

, GLENN E. STOLTZ. 

